U.S. patent number 9,523,285 [Application Number 14/105,951] was granted by the patent office on 2016-12-20 for energy storage systems with medium voltage electrical heat exchangers.
This patent grant is currently assigned to CHROMALOX, INC.. The grantee listed for this patent is Chromalox, Inc.. Invention is credited to Adam Heiligenstein, Christopher Molnar, Mark Wheeler.
United States Patent |
9,523,285 |
Heiligenstein , et
al. |
December 20, 2016 |
Energy storage systems with medium voltage electrical heat
exchangers
Abstract
Energy storage systems and methods use medium voltage (MV)
electrical heat exchangers to increase the efficiency of the energy
storage system and/or reduce emission of pollutants. MV electrical
heat exchangers use medium range voltages to heat a fluid, such as
a gas or liquid. The heated fluid is used in the energy storage
system to either drive a turbine generator directly or indirectly,
such as by generating steam to drive the turbine generator. The
electricity used to power the MV electrical heat exchangers can be
from renewable energy sources, such as solar or wind-powered
sources, further increasing efficiency of the energy storage
system.
Inventors: |
Heiligenstein; Adam (Gibsonia,
PA), Wheeler; Mark (Butler, PA), Molnar; Christopher
(Moon Township, PA) |
Applicant: |
Name |
City |
State |
Country |
Type |
Chromalox, Inc. |
Pittsburgh |
PA |
US |
|
|
Assignee: |
CHROMALOX, INC. (Pittsburgh,
PA)
|
Family
ID: |
52101605 |
Appl.
No.: |
14/105,951 |
Filed: |
December 13, 2013 |
Prior Publication Data
|
|
|
|
Document
Identifier |
Publication Date |
|
US 20150167489 A1 |
Jun 18, 2015 |
|
Current U.S.
Class: |
1/1 |
Current CPC
Class: |
H05B
3/50 (20130101); H02J 15/00 (20130101); F01K
5/02 (20130101); F01K 3/186 (20130101); F28D
20/00 (20130101); H02J 3/381 (20130101); F01D
15/10 (20130101); H02J 3/28 (20130101); F02C
6/16 (20130101); H02J 3/382 (20130101); Y02E
60/14 (20130101); F05D 2260/42 (20130101); Y02E
60/16 (20130101); H02J 2300/20 (20200101); H02J
2300/28 (20200101); Y02E 70/30 (20130101) |
Current International
Class: |
F01D
15/10 (20060101); F02C 6/16 (20060101); F28D
20/00 (20060101); H05B 3/50 (20060101); F01K
5/02 (20060101); F01K 3/18 (20060101); H02J
3/28 (20060101); H02J 15/00 (20060101) |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
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102011080830 |
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Feb 2013 |
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DE |
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1577549 |
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Sep 2005 |
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EP |
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2574756 |
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Apr 2013 |
|
EP |
|
2574784 |
|
Apr 2013 |
|
EP |
|
2657466 |
|
Oct 2013 |
|
EP |
|
WO 2013/006630 |
|
Jan 2013 |
|
WO |
|
Other References
International Search Report and Written Opinion for
PCT/US2014/067065 dated Mar. 19, 2015 (9 pages). cited by
applicant.
|
Primary Examiner: Denion; Thomas
Assistant Examiner: Mian; Shafiq
Attorney, Agent or Firm: K&L Gates LLP
Claims
What is claimed is:
1. An energy storage system comprising: a reservoir storing a fluid
for heating; a medium voltage electrical heat exchanger connected
to the reservoir for heating the fluid, wherein the medium voltage
electrical heat exchanger comprises one or more medium voltage
resistive heating elements, wherein each of the medium voltage
resistive heating elements is driven with a voltage between 601 V
and 69,000 V, inclusive; a turbine driven by the heated fluid; and
an electrical generator connected to the turbine for generating
electricity, wherein the one or more medium voltage resistive
heating elements each comprise: an outer metal sheath; a resistive
wire; and a dielectric core positioned within the outer metal
sheath, wherein the dielectric core comprises: a first series of
two or more axially-aligned, outer tubular dielectric bodies
positioned end-to-end; and a second series of two or more
axially-aligned, inner tubular dielectric bodies, wherein: the
inner tubular dielectric bodies are positioned end-to-end in the
sheath and are nested inside the outer tubular dielectric bodies;
the inner tubular dielectric bodies define an interior passageway
and the resistive wire is positioned in the interior passageway;
and the inner tubular dielectric bodies are longitudinally
staggered relative to the outer tubular dielectric bodies.
2. The energy storage system of claim 1, further comprising a
renewable energy source that supplies the voltage between 601 V and
69,000 V, inclusive, to the medium voltage resistive heating
elements of the medium voltage electrical heat exchanger to heat
the fluid.
3. The energy storage system of claim 1, wherein: the reservoir
comprises compressed gas as the fluid; and the compressed gas from
the reservoir flows to the medium voltage electrical heat
exchanger, whereupon the medium voltage electrical heat exchanger
heats the gas upon decompression of the gas; and the turbine is
powered by flow of the decompressed gas.
4. The energy storage system of claim 1, wherein: the reservoir
comprises a first tank; and the fluid in the first tank comprises
molten salt.
5. The energy storage system of claim 2, wherein the renewable
energy source comprises a wind-powered renewable energy source.
6. The energy storage system of claim 3, further comprising: a
compressor for compressing the gas for storage in the reservoir; an
auxiliary tank for storing a second fluid to be heated, wherein the
second fluid is heated with heat generated from compression of the
gas by the compressor; and a second medium voltage electrical heat
exchanger for heating the second fluid in the auxiliary tank,
wherein the second medium voltage electrical heat exchanger
comprises one or more medium voltage heating elements, wherein each
of the medium voltage resistive heating elements is driven with a
voltage between 601 V and 69,000 V, inclusive.
7. The energy storage system of claim 3, wherein the reservoir
comprises a tank.
8. The energy storage system of claim 3, wherein the reservoir
comprises an underground cavern.
9. The energy storage system of claim 4, wherein the medium voltage
electrical heat exchanger is powered by one or more photovoltaic
panels.
10. The energy storage system of claim 4, further comprising a
concentrated solar power receiver for heating the molten salt, and
wherein: the first tank stores the molten salt heated in the
concentrated solar power receiver; and the medium voltage
electrical heat exchanger is for heating the molten salt in the
first tank.
11. The energy storage system of claim 5, wherein the reservoir is
part of a pulverized coal-fired boiler.
12. The energy storage system of claim 6, wherein the second medium
voltage electrical heat exchanger is powered by a renewable energy
source.
13. The energy storage system of claim 9, the medium voltage
electrical heat exchanger is powered by DC voltage from the one or
more photovoltaic panels without converting the DC voltage to AC
voltage.
14. The energy storage system of claim 10, further comprising: a
steam generator for generating steam with the molten salt in the
first tank; a second tank for storing the molten salt after the
molten salt is used to generate the steam, wherein the molten salt
in the second tank is fed to the concentrated solar power receiver
for solar heating; and a second medium voltage electrical heat
exchanger for heating the molten salt in the second tank, wherein
the second medium voltage electrical heat exchanger comprises one
or more medium voltage resistive heating elements, wherein each of
the medium voltage resistive heating elements is driven with a
voltage between 601 V and 69,000 V, inclusive.
15. The energy storage system of claim 12, wherein the renewable
energy source comprises a wind-powered renewable energy source.
16. The energy storage system of claim 15, further comprising an
additional heat exchanger for heating the compressed gas prior to
heating by the medium voltage electrical heat exchanger, wherein
the additional heat exchanger uses heat from the second medium to
heat the compressed gas.
17. The energy storage system of claim 14, wherein the first and
second medium voltage electrical heat exchangers are powered by a
wind-power energy system.
18. A method for storing energy comprising: storing a fluid for
heating in a reservoir; heating the fluid with a medium voltage
electrical heat exchanger connected to the reservoir, wherein the
medium voltage electrical heat exchanger comprises one or more
medium voltage resistive heating elements, wherein each of the
medium voltage resistive heating elements is driven with a voltage
between 601 V and 69,000 V, inclusive, and wherein the one or more
medium voltage resistive heating elements each comprise: an outer
metal sheath; a resistive wire; and a dielectric core positioned
within the outer metal sheath, wherein the dielectric core
comprises: a first series of two or more axially-aligned, outer
tubular dielectric bodies positioned end-to-end; and a second
series of two or more axially-aligned, inner tubular dielectric
bodies, wherein: the inner tubular dielectric bodies are positioned
end-to-end in the sheath and are nested inside the outer tubular
dielectric bodies; the inner tubular dielectric bodies define an
interior passageway and the resistive wire is positioned in the
interior passageway; and the inner tubular dielectric bodies are
longitudinally staggered relative to the outer tubular dielectric
bodies; driving a turbine by the heated fluid; and generating
electricity with an electrical generator that is connected to the
turbine.
19. The method of claim 18, further comprising powering the medium
voltage electrical heat exchanger with a renewable energy source
that supplies the voltage between 601 V and 69,000 V, inclusive, to
the medium voltage resistive heating elements of the medium voltage
electrical heat exchanger to heat the fluid.
20. The method of claim 18, wherein: the reservoir comprises
compressed gas as the fluid; and the compressed gas from the
reservoir flows to the medium voltage electrical heat exchanger,
whereupon the medium voltage electrical heat exchanger heats the
gas upon decompression of the gas; and the turbine is powered by
flow of the decompressed gas.
21. The method of claim 18, wherein storing the fluid for heating
in a reservoir comprises storing molten salt in a reservoir that
comprises a first tank.
22. The method of claim 19, wherein the renewable energy source
comprises a wind-powered renewable energy source.
23. The method of claim 20, further comprising: compressing the gas
for storage in the reservoir with a compressor; storing a second
fluid to be heated in an auxiliary tank, wherein the second fluid
is heated with heat generated from compression of the gas by the
compressor; and heating the second fluid in the auxiliary tank with
a second medium voltage electrical heat exchanger, wherein the
second medium voltage electrical heat exchanger comprises one or
more medium voltage heating elements, wherein each of the medium
voltage resistive heating elements is driven with a voltage between
601 V and 69,000 V, inclusive.
24. The method of claim 21, further comprising powering the medium
voltage electrical heat exchanger with one or more photovoltaic
panels.
25. The method of claim 21, further comprising heating the molten
salt in a concentrated solar power receiver for, and wherein: the
first tank stores the molten salt heated in the concentrated solar
power receiver; and the medium voltage electrical heat exchanger is
for heating the molten salt in the first tank.
26. The method of claim 23, wherein the second medium voltage
electrical heat exchanger is powered by a wind-powered renewable
energy source.
27. The method of claim 25, further comprising: generating steam by
a steam generator using the molten salt in the first tank; storing
the molten salt in a second tank after the molten salt is used to
generate the steam, wherein the molten salt in the second tank is
fed to the concentrated solar power receiver for solar heating; and
heating the molten salt in the second tank with a second medium
voltage electrical heat exchanger, wherein the second medium
voltage electrical heat exchanger comprises one or more medium
voltage resistive heating elements, wherein each of the medium
voltage resistive heating elements is driven with a voltage between
601 V and 69,000 V, inclusive.
28. The method of claim 26, further comprising heating the
compressed gas with an additional heat exchanger for prior to
heating by the medium voltage electrical heat exchanger, wherein
the additional heat exchanger uses heat from the second medium to
heat the compressed gas.
29. The method of claim 27, further comprising powering the first
and second medium voltage electrical heat exchangers with a
wind-power energy system.
Description
BACKGROUND
The growth of renewable energy sources is driving the need for new
technologies to store electricity due to the random nature of the
availability of renewable power. For example, it is not always
sunny or windy; conversely, it may be sunny or windy when added
power it not needed on the power grid. There are currently a number
of techniques for storing electricity for later user. These energy
storage systems include: mechanical storage of energy via
compressed air or flywheel; electrical storage using super
capacitors or superconducting energy magnets; electromechanical
means such as various battery technologies; chemical storage by
producing hydrogen or synthetic natural gas; and thermal storage
where energy is either stored as hot water or molten salt, or used
to change the phase of a material.
While providing renewable energy benefits, many of the systems are
inefficient in various ways and/or have deleterious effects. For
example, compressed air energy storage (CAES) systems often use
natural gas to heat the compressed air upon decompression, which
results in the emission of air pollution in the form of NO.sub.x
and CO.sub.2. Also, hot water energy systems also often use gas or
coal to heat the large quantities of water that is needed to the
desired temperature, which are non-renewable energy sources.
SUMMARY
In one general aspect, the present invention is directed to energy
storage systems that use medium voltage (MV) electrical heat
exchangers to increase the efficiency of the energy storage system
and/or reduce emission of pollutants. MV electrical heat exchangers
use medium range voltages, i.e., 601 to 69,000 volts, to heat a
fluid, such as a gas or liquid. The heated fluid is used in the
energy storage system to either drive a turbine generator directly
or indirectly, such as by generating steam to drive the turbine
generator. MV electrical heat exchangers are advantageous because
nearly 100% of the energy produced is absorbed directly by the
heated fluid, allowing for very efficient conversion of electricity
into heat. Furthermore, the electricity used to power the MV
electrical heat exchangers can be from renewable energy sources,
such as solar or wind-powered sources, further increasing
efficiency of the energy storage system.
FIGURES
Various embodiments of the present invention are described herein
by way of example in conjunction with the following figures,
wherein:
FIGS. 1 and 2 illustrate aspect of a medium voltage resistive
heating element according to various embodiments of the present
invention;
FIGS. 3 and 4 illustrate different medium voltage heat
exchangers;
FIG. 5 illustrates a prior art compressed air energy storage
system;
FIG. 6 illustrates a compressed air energy storage system according
to various embodiments of the present invention;
FIG. 7 illustrates a coal-fired energy storage system according to
various embodiments of the present invention;
FIG. 8 illustrates a concentrated solar power energy storage system
according to various embodiments of the present invention; and
FIG. 9 illustrates a photovoltaic energy storage system according
to various embodiments of the present invention.
DESCRIPTION
In one general aspect, the present invention is directed to energy
storage systems that use medium voltage (MV) electrical heating
systems or heat exchangers (MVHEs). MV heaters are metal-sheathed
resistive heating elements that operate at voltages from 601 volts
to 69,000 volts, for example. MV heating provides tremendous
efficiencies in converting electricity to heat in comparison to
traditional low voltage (LV) systems. For example, a LV system
operating at 480 VAC and producing 1 megawatt of heat would require
of 1200 amps, which would be cost prohibitive. On the other hand, a
MV system producing 1 megawatt of heat, but operating at 4160 VAC,
would require only approximately 140 amps of power. This lower
amperage lowers the overall equipment costs and eliminates the need
for large power transformers that would be required to reduce the
voltage down to 480 VAC to operate the heaters in a LV system.
The MVHEs used in the various energy storage systems may comprise
one or more MV heating elements. FIGS. 1-2 are diagrams of a MV
heating element 20 according to various embodiments. As shown in
the example of FIGS. 1 and 2, the MV heating element can include an
outer, cylindrical sheath 22 that defines an opening that houses a
dielectric core 50 and resistive wires, which inside insulative
sleeves 66a, 66b. In various embodiments, the outer sheath 22 can
comprise a tube and/or sleeve, for example, which can at least
partially encase and/or enclose the heat generating components of
the electric heating element assembly 20, i.e., the resistive wires
62a, 62b (see FIG. 2). The outer sheath 22 can be a metallic tube,
for example, such as a tube comprised of steel, stainless steel,
copper, incoloy, inconel and/or hasteloy, for example. The
dielectric core 50 can comprise a dielectric material, such as
boron nitride (BN), aluminum oxide (AlO), magnesium oxide (MgO),
ceramic material, etc. In various embodiments, multiple nested,
staggered core segments can be used to reduce dielectric breakdown
and/or arcing. Such MV heater elements are described in U.S. patent
application Ser. No. 13/802,842, entitled "Medium Voltage Heating
Element Assembly," by Chromalox Inc., filed Mar. 13, 2013 ("the
'842 application"), which is incorporated herein by reference in
its entirety.
As explained in the '842 application, and as shown in FIG. 2, the
insulative sleeves 66a, 66b may surround the heat-generating
resistive coils 62a, 62b. The resistive coils 62a, 62b can be
connected together by a u-shaped wire 62c at the distal end 26 of
the heating element 20. A leadwire (not shown) and/or a conductor
pin 64a, 64b can extend from each resistive coil 62a, 62b through
the electric heating element assembly 20. The leadwire and/or the
conductor pin 64a, 64b can conduct current from a power source to
the resistive coil 62a, 62b coupled thereto to generate heat. The
power source can supply 601 to 69,000 volts (AC or DC), for
example. As also explained in the '482 application and as shown in
FIG. 2, the dielectric core 50 may comprise inner and outer
annular, staggered core segments 32a-d (outer), 42a-d (inner) to
prevent and/or reduce the likelihood of dielectric breakdown and/or
arcing at the interfaces between adjacent core segments, for
example. As a result, current may be less inclined to attempt to
flow through the indirect, stepped path between the inner core 40
and the outer core 30, and thus, the stepped interface formed by
the staggered boundaries 38, 48 can prevent and/or reduce the
likelihood of dielectric breakdown and/or arc. Furthermore, in
various embodiments, the electric heating element assembly 20 can
include additional powdered and/or particulate dielectric material
within the outer sheath 22. Such dielectric material can settle at
the boundaries 38, 48 between various elements of the dual core 28,
in faults, voids, and/or cracks of the various dual core 28
elements, and/or between the dual core 28 and various other
components of the electric heating element assembly 20, such as,
for example, the outer sheath 22, a termination bushing 50, and/or
a termination disk 70. In various embodiments, the bushing 50 can
prevent and/or reduce the likelihood of arcing between multiple
leadwires and/or conductor pins 64a, 64b and the sheath 22.
Further, because moisture that accumulates in MV heating elements
can cause failure, MV heating elements that employ a moisture
sensor and control the heating element, particularly at start up,
based on the detected moisture in the heating element, may be used.
One such MV heating element control circuit is disclosed in U.S.
patent application Ser. No. 13/866,434, entitled "Medium Voltage
Heater Elements Moisture Detection Circuit," by Chromalox Inc.,
filed Apr. 19, 2013, which is incorporated herein by reference in
its entirety.
Such MV heating elements 20 can be used in MVHEs that are used in
energy storage systems according to various embodiments of the
present invention. The MVHE could be, for example, a flanged
immersion heater 100 as shown in FIG. 3 or a circulation heater 120
as shown in FIG. 4. The flanged immersion heater 100 comprises one
or more MV heating elements 20 connected to a flange 102. The
heating elements 20 of the immersion heater 100 can be immersed
into the fluid to be heated (gas or liquid) when stored in a
storage tank 104. The flange 102 can be connected to a wall of the
storage tank 104 so that the heating elements 20 extend into the
fluid inside the tank to heat the fluid. A circulation heater 120
as shown in FIG. 4 may include one or more MV heating elements 20
inside a chamber 122. The circulation heater 120 may be connected
to (but not immersed in) a storage tank that includes the fluid to
be heated. The fluid can flow out of the storage tank, into the
chamber 122 of the circulation heater 120 via an inlet pipe 124 to
be heated, and then flow out of the circulation heater 120 via an
outlet pipe 126 back into the storage tank. The fluid may be pumped
continuously through the circulation heater 120 to keep the fluid
at the desired temperature.
MVHEs are advantageous to other MV heating technologies as MVHEs
can be inserted directly into the heated fluid (e.g., gases, air,
water, molten salt, etc.), with nearly 100% of the energy produced
being absorbed directly by the fluid, allowing for very efficient
conversion of electricity into heat. This enables a smart power
grid by allowing the opportunity to store a precise amount of
energy from the network at specific times. Such energy storages
systems are described below.
FIG. 5 is a simplified block diagram of a known type of compressed
air energy storage (CAES) system 150. Air is compressed by a
compressor 152 and the compressed air is stored in a storage tank
154. In such systems the storage 154 is usually underground. Also,
instead of a tank, some CAES systems utilize underground caverns to
store the compressed air. The heat generated by compression of the
air by the compressor 152 may be extracted by a heat exchanger 156
to heat a fluid (e.g., gas or liquid) stored in a thermal storage
tank 158. The thermal energy from the thermal storage tank 158
could be used to generate electricity when needed. When needed, the
compressed air in the storage tank 154 can be used to generate
electricity by, in most current CAES systems, heating the
compressed air upon decompression with a gas re-heater system 162
to drive a turbine 164 to power a generator 166 to generate
electricity that can be supplied to the power grid (not shown). The
gas re-heaters 162 typically use natural gas and emit air pollution
in the form of NO and CO.sub.2.
FIG. 6 is a block diagram of a CAES system 180 using a MV
electrical heat exchanger according to embodiments of the present
invention. The CAES system 180 of FIG. 6 is similar to the system
150 of FIG. 5, except that the gas re-heater 162 is FIG. 5 is
replaced with a MV electrical heat exchanger 182 in the CAES system
180 of FIG. 6. The MV electrical heat exchanger 182 in such an
embodiment could be a circulation heater that heats the
decompressed air for driving the turbine 162, and could be powered
by a MV source 184 (which could be either AC or DC). Using the MV
electrical heat exchanger 182 eliminates the need for the gas
re-heater 162 in the CAES system 150 in FIG. 5, and thereby
eliminates the air pollution generated by the gas re-heater 162.
Also as shown in FIG. 6, another MV electrical heat exchanger 186
may be used to supply additional heat for the fluid in the thermal
storage tank. The MV electrical heat exchanger 186 could be
implemented as an immersion heater, and could be power by a
renewable energy source 188, such as a solar or wind energy source.
That way, the thermal energy storage tank 158 could be heated
additionally with the heat from the MV electrical heat exchanger
186 at low cost since it is powered by a renewable energy source
188. The heat from the thermal energy storage tank 158 could then
be used to reheat the decompressing gasses with a heat exchanger
189.
MV heaters could also be used in coal power plants according to
various embodiments. Because of decreased demand at night, coal
power plants are typically cycled back to far less than full
capacity, to about 20%, during the night, which is still more than
required by the nighttime demand. The system cannot ordinarily be
totally shut down at night because it would not have enough time to
ramp up when demand increases in the morning, thereby making
operation during the off-peak night hours inefficient. FIG. 7 is a
diagram of a coal-power electricity generation plant 200 that
utilizes a MV electrical heat exchanger 202 in the plant's
pulverized coal-fired boiler 204. The boiler 204 generates thermal
energy by burning pulverized coal, from a pulverizer 206. The
boiler 204 generates steam to drive a turbine 208, which in turn
drives a generator 201 to supply electricity to the power grid. The
MV electrical heat exchanger 202 could be powered at night by
excess energy on the power grid and/or renewable energy sources
(i.e., wind energy) to keep the water in the boiler 204 heated.
That way, the coal-heating in the boiler 204 could be reduced even
more at night, thereby conserving coal, and with the thermal energy
from the MV electrical heat exchanger 202 stored, in the form of
the heated water in the boiler, to generate electricity when need
in the morning. Such a coal-powered energy system could especially
benefit from being located near an under-utilized wind energy power
system 212. That way, the excess energy from the wind energy power
system could be used to power the MV electrical heat exchanger 202
to thereby reduce the operating capacity of the coal-fired boiler
204. In such an embodiment, the MV electrical heat exchanger 202
may be implemented as an immersion heater.
MV heaters could also be used in molten salt energy storage
systems. FIG. 8 is a simplified diagram of a molten salt energy
storage system 250. In such a system, sunlight is directed by
heliostats 252 to a receiver 254 storing molten salt atop a tower
256. When the molten salt is solar heated to a sufficiently high
temperature, e.g., around 570.degree. C., it is stored in a hot
salt storage tank 258. The hot molten salt can then be used as
needed by a steam generator 260 to generate steam, which powers a
turbine generator 262 to generate electricity. The cooled molten
salt, at around 290.degree. C., cooled from the steam generation
process, is stored in a cold salt storage tank 264 and eventually
returned to the receiver 254 to restart the process. At night, when
the sun is not shining, a MV electrical heat exchanger 270 can be
used to heat molten salt in the hot salt storage tank 258. Such a
MV electrical heat exchanger 270 could be implemented as an
immersion or circulation heater, and is powered by the MV source
272. The MV source 272 could be a renewable energy source, such as
a wind power source, so that the wind energy could be used to heat
the salt in the hot salt storage tank 258 during the night when it
cannot be heated with solar energy. That way, the plant could start
running sooner in the morning when the demand for electricity
rises, even when the sun is not yet shining. Similarly, a MV
electrical heat exchanger 274 could be used to heat the salt in the
cold salt storage tank 260, again with voltage supplied by the MV
source 272. That way, the salt in the receiver 254 will be warmer
than without the MV electrical heat exchanger 274 in the cold salt
storage tank 260, thereby reducing the time it takes the
concentrated solar energy to heat the salt in the receiver 254
during the day to the desired temperature to run the generator
262.
FIG. 9 is a simplified block diagram of a photovoltaic energy
system 300 that uses a MV electrical heat exchanger according to
various embodiments of the present invention. In the illustrated
embodiment, a storage tank 304 stores a fluid 306, such as water,
oil, other phase-change materials, molten salt, etc. Where the
fluid 306 is a phase-change material such as water/steam, the gas
(e.g., steam) from the heated fluid can be used to drive a turbine
308 that drives an electricity generator 310. Where the fluid 306
is not a phase-change material (e.g., molten salt), the heated
fluid 306 can be used to generate steam by a steam generator 312,
that can be used to drive the turbine 308.
As shown in FIG. 9, the MV electrical heat exchanger 302 is powered
with voltage from a photovoltaic panel(s) 314. Such a photovoltaic
panel(s) 314 generates DC electricity, which is normally converted
to AC in many applications. Here, however, the DC electricity from
the photovoltaic panel(s) 314 does not need to be converted to AC
as the MV electrical heat exchanger 302 can be powered by DC,
thereby eliminating the need for an inverter. In other embodiments,
however, the MV electrical heat exchanger 302 could be powered by
AC, in which case an inverter (not shown) could be used to convert
the DC power from the photovoltaic panel(s) 314 to AC to power the
MV electrical heat exchanger 302.
A shortcoming of photovoltaic panels is the fast-changing nature of
its output (e.g., due to passing clouds), which has a destabilizing
effect on the power grid. Converting the electrical energy from the
photovoltaic panel(s) 314 to heat with the MV electrical heat
exchanger 302, as shown in FIG. 9, maintains the energy and tends
to level its output. When the sun energy is lost due to clouds or
night, the heat in the molten salt (or other fluid) 306 can
continue to provide electrical power generation.
In general aspect, therefore, the present invention is directed to
energy storage systems and methods. According to various
embodiments, the energy storage system comprises a reservoir
storing a fluid for heating (e.g., a tank or underground cavern)
and a medium voltage electrical heat exchanger connected to the
reservoir for heating the fluid. The medium voltage electrical heat
exchanger comprises one or more medium voltage resistive heating
elements, where each of the medium voltage resistive heating
elements is driven with a voltage between 601 V and 69,000 V,
inclusive. The energy system also comprises a turbine driven by the
heated fluid (either directly or indirectly) and an electrical
generator connected to the turbine for generating electricity. The
energy system may further comprise a renewable energy source (e.g.,
a wind-powered renewable energy source) that supplies the voltage
between 601 V and 69,000 V, inclusive, to the medium voltage
resistive heating elements to heat the fluid.
In various implementations, as shown in FIG. 6, the reservoir 154
comprises compressed gas as the fluid, in which case the compressed
gas from the reservoir 154 flows to the medium voltage electrical
heat exchanger 182, whereupon the medium voltage electrical heat
exchanger 182 heats the gas upon decompression of the gas, and the
turbine 164 is powered by flow of the decompressed gas. Such an
energy storage system may further comprise a compressor 152 for
compressing the gas for storage in the reservoir 154; an auxiliary
tank 158 for storing a second fluid to be heated, where the second
fluid is heated with heat generated from compression of the gas by
the compressor 152; and a second medium voltage electrical heat
exchanger 186 for heating the second fluid in the auxiliary tank
158. Also, the second medium voltage electrical heat exchanger 186
may be powered by a renewable energy source 188, such as a
wind-powered renewable energy source. The energy storage system may
further comprise an additional heat exchanger 189 for heating the
compressed gas prior to heating by the medium voltage electrical
heat exchanger 182, where the additional heat exchanger 189 uses
heat from the second medium in the auxiliary tank 158 to heat the
compressed gas.
In other implementations, the reservoir is part of a pulverized
coal-fired boiler 204, as shown in FIG. 7, or a first tank 258, 304
that stores molten salt as part of a molten salt energy storage
system, as shown in FIGS. 8 and 9. In a molten salt energy storage
system, as shown in FIG. 9, the medium voltage electrical heat
exchanger 302 may be powered by one or more photovoltaic panels
314. This can also be done without converting the DC voltage from
the photovoltaic panel(s) to AC voltage. In other molten salt
energy storage system embodiments, as shown in FIG. 8, a
concentrated solar power receiver 254 heats the molten salt and the
first tank 258 stores the molten salt heated in the concentrated
solar power receiver. The medium voltage electrical heat exchanger
270 is for heating the molten salt in the first tank 258. Also, the
system may comprise a steam generator 260 for generating steam with
the molten salt in the first tank, a second tank 260 for storing
the molten salt after the molten salt is used to generate the
steam, where the molten salt in the second tank 260 is fed to the
concentrated solar power receiver 254 for solar heating, and a
second medium voltage electrical heat exchanger 274 for heating the
molten salt in the second tank 260. Again, the first and second
medium voltage electrical heat exchangers 270, 274 may be powered
by a wind-power energy system 272.
In one general aspect, the method for storing energy may comprise
the steps of: (i) storing a fluid for heating in a reservoir (e.g.,
reservoirs 154, 204, 258 or 304); (ii) heating the fluid with a
medium voltage electrical heat exchanger 182, 202, 270, 302
connected to the reservoir; (iii) driving, indirectly or directly,
a turbine 164, 208, 262, 312 by the heated fluid; and (iv)
generating electricity with an electrical generator 166, 210, 262,
310 that is connected to the turbine.
One skilled in the art will recognize that the herein described
components (e.g., operations), devices, objects, and the discussion
accompanying them are used as examples for the sake of conceptual
clarity and that various configuration modifications are
contemplated. Consequently, as used herein, the specific exemplars
set forth and the accompanying discussion are intended to be
representative of their more general classes. In general, use of
any specific exemplar is intended to be representative of its
class, and the non-inclusion of specific components (e.g.,
operations), devices, and objects should not be taken limiting.
With respect to the use of substantially any plural and/or singular
terms herein, those having skill in the art can translate from the
plural to the singular and/or from the singular to the plural as is
appropriate to the context and/or application. The various
singular/plural permutations are not expressly set forth herein for
sake of clarity.
The herein described subject matter sometimes illustrates different
components contained within, or connected with, different other
components. It is to be understood that such depicted architectures
are merely exemplary, and that in fact many other architectures may
be implemented which achieve the same functionality. In a
conceptual sense, any arrangement of components to achieve the same
functionality is effectively "associated" such that the desired
functionality is achieved. Hence, any two components herein
combined to achieve a particular functionality can be seen as
"associated with" each other such that the desired functionality is
achieved, irrespective of architectures or intermedial components.
Likewise, any two components so associated can also be viewed as
being "operably connected," or "operably coupled," to each other to
achieve the desired functionality, and any two components capable
of being so associated can also be viewed as being "operably
couplable," to each other to achieve the desired functionality.
While particular aspects of the present subject matter described
herein have been shown and described, it will be apparent to those
skilled in the art that, based upon the teachings herein, changes
and modifications may be made without departing from the subject
matter described herein and its broader aspects and, therefore, the
appended claims are to encompass within their scope all such
changes and modifications as are within the true spirit and scope
of the subject matter described herein. It will be understood by
those within the art that, in general, terms used herein, and
especially in the appended claims (e.g., bodies of the appended
claims) are generally intended as "open" terms (e.g., the term
"including" should be interpreted as "including but not limited
to," the term "having" should be interpreted as "having at least,"
the term "includes" should be interpreted as "includes but is not
limited to," etc.). It will be further understood by those within
the art that if a specific number of an introduced claim recitation
is intended, such an intent will be explicitly recited in the
claim, and in the absence of such recitation no such intent is
present. For example, as an aid to understanding, the following
appended claims may contain usage of the introductory phrases "at
least one" and "one or more" to introduce claim recitations.
However, the use of such phrases should not be construed to imply
that the introduction of a claim recitation by the indefinite
articles "a" or "an" limits any particular claim containing such
introduced claim recitation to claims containing only one such
recitation, even when the same claim includes the introductory
phrases "one or more" or "at least one" and indefinite articles
such as "a" or "an" (e.g., "a" and/or "an" should typically be
interpreted to mean "at least one" or "one or more"); the same
holds true for the use of definite articles used to introduce claim
recitations.
In addition, even if a specific number of an introduced claim
recitation is explicitly recited, those skilled in the art will
recognize that such recitation should typically be interpreted to
mean at least the recited number (e.g., the bare recitation of "two
recitations," without other modifiers, typically means at least two
recitations, or two or more recitations). Furthermore, in those
instances where a convention analogous to "at least one of A, B,
and C, etc." is used, in general such a construction is intended in
the sense one having skill in the art would understand the
convention (e.g., "a system having at least one of A, B, and C"
would include but not be limited to systems that have A alone, B
alone, C alone, A and B together, A and C together, B and C
together, and/or A, B, and C together, etc.). In those instances
where a convention analogous to "at least one of A, B, or C, etc."
is used, in general such a construction is intended in the sense
one having skill in the art would understand the convention (e.g.,
"a system having at least one of A, B, or C" would include but not
be limited to systems that have A alone, B alone, C alone, A and B
together, A and C together, B and C together, and/or A, B, and C
together, etc.). It will be further understood by those within the
art that typically a disjunctive word and/or phrase presenting two
or more alternative terms, whether in the description, claims, or
drawings, should be understood to contemplate the possibilities of
including one of the terms, either of the terms, or both terms
unless context dictates otherwise. For example, the phrase "A or B"
will be typically understood to include the possibilities of "A" or
"B" or "A and B."
With respect to the appended claims, those skilled in the art will
appreciate that recited operations therein may generally be
performed in any order. Also, although various operational flows
are presented in a sequence(s), it should be understood that the
various operations may be performed in other orders than those
which are illustrated, or may be performed concurrently. Examples
of such alternate orderings may include overlapping, interleaved,
interrupted, reordered, incremental, preparatory, supplemental,
simultaneous, reverse, or other variant orderings, unless context
dictates otherwise. Furthermore, terms like "responsive to,"
"related to," or other past-tense adjectives are generally not
intended to exclude such variants, unless context dictates
otherwise.
Although various embodiments have been described herein, many
modifications, variations, substitutions, changes, and equivalents
to those embodiments may be implemented and will occur to those
skilled in the art. Also, where materials are disclosed for certain
components, other materials may be used. It is therefore to be
understood that the foregoing description and the appended claims
are intended to cover all such modifications and variations as
falling within the scope of the disclosed embodiments. The
following claims are intended to cover all such modification and
variations.
In summary, numerous benefits have been described which result from
employing the concepts described herein. The foregoing description
of the one or more embodiments has been presented for purposes of
illustration and description. It is not intended to be exhaustive
or limiting to the precise form disclosed. Modifications or
variations are possible in light of the above teachings. The one or
more embodiments were chosen and described in order to illustrate
principles and practical application to thereby enable one of
ordinary skill in the art to utilize the various embodiments and
with various modifications as are suited to the particular use
contemplated. It is intended that the claims submitted herewith
define the overall scope.
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